The present invention relates generally to temperature compensation systems, and more specifically to temperature compensation systems for minimizing offset variations in a sensor sensing an operating condition of an internal combustion engine.
Modern electronic control systems for internal combustion engines include a number of sensors and/or sensing systems for determining various engine operating conditions. Many of these sensors are located in harsh environments and are subjected to widely varying operating conditions throughout their lives. Despite potentially harsh operating conditions, however, such sensors are typically required to produce consistent results over their entire operating range.
An example of one varying environmental condition that many engine operating condition sensors are subject to is temperature. Typically, many engine operating condition sensors are required to operate consistently over a wide temperature range that may include temperatures as low as xe2x88x9240xc2x0 C. and as high as 150xc2x0 C. While some engine operating condition sensors tend to operate substantially consistently over a required operating temperature ranges, others do not, Even with those that do not, performance specifications of some such sensors may allow for wide variations in sensor operation over temperature, and in such cases, temperature compensation of the resultant sensor signal is typically not warranted.
One solution to the problem of varying sensor operation over temperature is to design the sensor to be robust over temperature and therefore less susceptible to temperature fluctuations. This, however, is typically a costly solution, and designers of engine control systems have accordingly opted for less costly solutions such as temperature compensation of the raw sensor signal. Although typically less costly, conventional temperature compensation schemes for engine operating condition sensors have their own drawbacks. For example, the sensor may exhibit a complicated temperature response that is difficult to model or to counteract with temperature compensation circuitry. Further, the sensor temperature response may vary widely from sensor to sensor. Further still, only a portion of the sensor signal; i.e., either a sensitivity (signal gain) term or a DC offset term, may be susceptible to temperature-induced variations while other portions of the signal are substantially temperature independent. What is therefore needed is a temperature compensation system for minimizing sensor signal variations that addresses these and other drawbacks associated with known sensor compensation strategies.
The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, a temperature compensation system for minimizing sensor offset variations comprising: a sensor producing a sensor signal indicative of an operating condition of an internal combustion engine, means for determining a temperature of said sensor and producing a temperature signal corresponding thereto, a key switch for starting and stopping said engine, said key switch having at least an on position and an off position, and an engine controller responsive to a transition of said key switch to said on position to determine a first temperature signal value and an associated first sensor signal value, said controller responsive to a transition of said key switch to said off position to determine a second temperature signal value and an associated second sensor signal value, said controller defining an offset value associated with said sensor as a function of said first and second temperature signal values and of said first and second sensor signal values.
In accordance with another aspect of the present invention, a temperature compensation system for minimizing sensor offset variations comprises a sensor producing a sensor signal indicative of an operating condition of an internal combustion engine, a memory having stored therein a model of said operating condition, said model defining a temperature dependent offset term, means for determining a temperature of said sensor and producing a temperature signal corresponding thereto, a key switch for starting and stopping said engine, said key switch having at least an on position and an off position, and an engine controller monitoring said key switch, said controller responsive to said temperature signal and said sensor signal to determine a first temperature and a first signal value associated with said sensor if said key switch switches to either of said off and on positions, said controller updating said temperature dependent offset term based on said first temperature and said first signal value.
In accordance with a further aspect of the present invention, a temperature compensation method of minimizing sensor offset variations comprises the steps of sensing an operating condition of an internal combustion engine with an engine operating condition sensor, computing a value of said engine operating condition based on a model defining a response of said engine operating condition sensor, said model including a temperature dependent offset term, monitoring a key switch for starting and stopping said engine, determining a first operating temperature of said engine operating condition sensor and an associated first sensor value if said key switch switches to either of an off and an on position thereof, and updating said offset term of said model based on said first operating temperature and said first sensor value.
One object of the present invention is to provide a temperature compensation system for minimizing variations in a sensor offset parameter.
Another object of the present invention is to provide such a system for temperature compensating an offset term of an engine operating condition sensor.
A further object of the present invention is to provide such a system for temperature compensating an offset term of a differential pressure sensor in particular, wherein the sensor is disposed across a flow restriction mechanism disposed between an exhaust manifold and an intake manifold of the engine.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiments.